1. Field of the Invention
An aircraft having high aspect ratio wings and a lifting-body fuselage.
2. Discussion of the Background
Airplanes which have wings of high aspect ratio (AR) typically have tubular fuselages of circular or oval cross section that provide negligible portions of the lift. Many proposals have been made to enhance the airplane's ability to generate lift by giving the fuselage an airfoil shape. Taking this idea to its extreme results in the Northrop "flying wing" designs which have no fuselage or tail in the conventional sense. Flying wings have a serious limitation in that they are relatively short in length, so pitch control surfaces at the rear do not have enough leverage to handle normal shifts in the location of the center of gravity. In general, the CG range of a pure flying wing is so limited that its mission must be highly specialized.
A number of designs have been proposed which combine a distinct lifting-fuselage with a distinct high aspect ratio wing. This type generally has a pitch control surface located far enough behind the aircraft's center of gravity that it has a large CG range. A series of such lifting-fuselage/wing airplanes were designed and built in the United States by Vincent Burnelli in the 1920's and 1930's and described in U.S. Pat. Nos. 1,780,813; 2,380,289; 2,380,290; 2,616,639 and D 198,610. In 1936 the Burnelli UB14B transport aircraft was produced with a high aspect ratio wing and an airfoil-shaped fuselage holding the flight crew and fourteen passengers. Other patents describing lifting-fuselage/wing aircraft include U.S. Pat. No. 3,869,102 (Carroll); U.S. Pat. No. 3,216,673 (Alter et al); U.S. Pat. No. 2,734,701 (Horton); U.S. Pat. No. 3,630,471 (Fredricks) and U.S. Pat. No. 4,146,199 (Wenzell). Few such aircraft have been built and none has been very successful.
A widely cited reason for the failure of early lifting-fuselage/wing airplanes is that the configuration necessarily has more drag than conventional airplanes. That is because a lifting fuselage constitutes a wing of low aspect ratio, and it is well known that the lift to drag ratio (L/D) of a wing decreases as its aspect ratio decreases. This effect is due mainly to an increase in the induced drag (drag due to lift) which occurs as the span is reduced. Therefore, any additional lift produced by a fuselage would add more induced drag than simply enlarging the wing would do. Because of this fundamental problem, there has not been much recent interest in lifting-fuselage/wing designs. An article in the April 1994 edition of Flying magazine stated
The lifting fuselage is one of those popular misconceptions that never die. When an airplane has a long skinny wing going one way and a long skinny fuselage going the other, lift from the fuselage is no virtue, because it can only be produced at a very high price in induced drag, and besides it can only be destabilizing. It's no accident that all modern airliners have fuselages consisting of a cylindrical central section with a streamlined nose and tail. If there were something to be gained by giving the fuselage the profile of an airfoil, Boeing et al would have done so. PA1 (i) the aircraft has a cruise design point in which the fuselage lift coefficient (C.sub.LF) is 0.08 or less, and PA1 (ii) the fuselage lift coefficient is at least 0.50 at an angle of attack (.alpha..sub.LZo) of 10.degree., in level flight at sea level (ISA) with all moveable lift enhancing devices retracted.
This argument is valid when the fuselage is narrow. However, if the body is made extremely wide there is something to be gained by giving it the profile of an airfoil. Such a body can produce large amounts of lift at high angles of attack; enough lift to replace one or more of the usual high-lift devices, e.g., wing flaps, yet retain the ability to fly at slow speeds. But that benefit alone would not outweigh the penalties if the fuselage added too much induced drag at cruise speeds. The present invention solves that problem.